Method of manufacturing a printed circuit board assembly sheet

ABSTRACT

A dummy trace portion is provided in a region between at least a suspension board with circuit on one end side and a support frame of a suspension board assembly sheet with circuits. A base insulating layer is formed on a support substrate in the dummy trace portion. A plurality of conductor traces are formed on the base insulating layer, and a cover insulating layer is formed on the base insulating layer to cover each conductor trace. At least one of the base insulating layer and the cover insulating layer in the dummy trace portion has a groove.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. Patent Application No.13/189,612, filed Jul. 25, 2011, which claims the benefit of U.S.Provisional Patent Application No. 61/378,091, filed Aug. 30, 2010, andthe disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board assembly sheetand a method of manufacturing the same.

2. Description of the Background Art

Actuators are employed in drives such as hard disk drives. Such anactuator includes an arm arranged rotatably with respect to a rotationshaft and a suspension board with circuit for a magnetic head that isattached to the arm. The suspension board with the circuit is a printedcircuit board for positioning the magnetic head with a desired track ofa magnetic disk.

In manufacturing steps of such a suspension board with circuit, aplurality of assembly sheets each including suspension boards withcircuits (hereinafter referred to as suspension board assembly sheetswith circuits) are formed on a metal support substrate. The supportsubstrate is then cut, so that the suspension board assembly sheets withcircuits are separated from one another. A plurality of suspensionboards with circuits are arranged in alignment within a rectangularsupport frame in the suspension board assembly sheet with circuits (seeJP 2007-109725 A and JP 2007-115828 A, for example). Finally, each ofthe suspension boards with circuits is separated from the suspensionboard assembly sheet with circuits.

Preparing the suspension board assembly sheet with circuits makes iteasy to handle the plurality of suspension boards with circuits.However, each of the suspension board assembly sheets with circuits cutand separated from the support substrate may be warped. Thus, each ofthe suspension boards with circuits that are to be separated from thesuspension board assembly sheet with circuits may also be warped in thefinal manufacturing step.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a printed circuit boardassembly sheet that is inhibited from being warped and a method ofmanufacturing the same.

(1) According to one aspect of the present invention, a printed circuitboard assembly sheet includes a plurality of printed circuit boards, asupport frame configured to integrally support the plurality of printedcircuit boards such that the plurality of printed circuit boards arearranged at spacings, and a dummy trace portion provided in a regionbetween at least a printed circuit board on one end side and the supportframe, wherein each of the plurality of printed circuit boards and thedummy trace portion includes a support substrate, a first insulatinglayer formed on the support substrate, a plurality of conductor tracesformed on the first insulating layer, and a second insulating layerformed on the first insulating layer to cover the plurality of conductortraces, and at least one of the first and second insulating layers inthe dummy trace portion has a groove.

In the printed circuit board assembly sheet, the at least one of thefirst and second insulating layers in the dummy trace portion has thegroove. This reduces residual stress in the at least one of the firstand second insulating layers in the dummy trace portion. As a result,the printed circuit board assembly sheet is inhibited from being warped.

(2) The groove may be formed in the second insulating layer in a regionbetween adjacent conductor traces in the dummy trace portion.

In this case, the thickness of the region between the conductor tracesis smaller than the thickness of other portions. This sufficientlyreduces residual stress in the region between the conductor traces. As aresult, the printed circuit board assembly sheet is sufficientlyinhibited from being warped.

(3) The groove may be formed in the first insulating layer in a regionbetween adjacent conductor traces in the dummy trace portion.

In this case, the thickness of the region between the conductor tracesis smaller than the thickness of other portions. This sufficientlyreduces residual stress in the region between the conductor traces. As aresult, the printed circuit board assembly sheet is sufficientlyinhibited from being warped.

(4) An opening may be further formed in the support substrate in thedummy trace portion. In this case, residual stress is also reduced inthe opening of the support substrate in the dummy trace portion. Thissufficiently inhibits the printed circuit board assembly sheet frombeing warped.

(5) The support frame may have a pair of first frame portions that aresubstantially parallel to each other, and a pair of second frameportions that are substantially perpendicular to the first frameportions, and the plurality of printed circuit boards are provided to bearranged in a direction parallel to the pair of first frame portions,and the dummy trace portion may be provided in a region between at leastthe printed circuit board on the one end side and one of the pair ofsecond frame portions, and the conductor traces and the groove in thedummy trace portion may be formed to extend in a direction from one ofthe first frame portions to the other one of the first frame portions.

In this case, the residual stress in the direction from the one of thefirst frame portions toward the other one of the first frame portions inthe dummy trace portion is reduced. This inhibits the pair of secondframe portions from being warped.

(6) The printed circuit board may be a suspension board with circuit. Inthis case, the printed circuit board assembly sheet including theplurality of suspension boards with circuits is inhibited from beingwarped. Thus, flatness is ensured in the plurality of suspension boardswith circuits. This improves the manufacture yield of the plurality ofsuspension boards with circuits.

(7) According to another aspect of the present invention, a method ofmanufacturing a printed circuit board assembly sheet that includes aplurality of printed circuit boards, a support frame configured tointegrally support the plurality of printed circuit boards such that theplurality of printed circuit boards are arranged at spacings, and adummy trace portion provided in a region between at least a printedcircuit board on one end side and the support frame includes the stepsof forming first insulating layers, which correspond to the plurality ofprinted circuit boards and the dummy trace portion, on a supportsubstrate, forming a plurality of conductor traces on each of the firstinsulating layers corresponding to the plurality of printed circuitboards and the first insulating layer corresponding to the dummy traceportion, and forming second insulating layers on the first insulatinglayers to cover the plurality of conductor traces corresponding to theplurality of printed circuit boards and the conductor tracecorresponding to the dummy trace portion, respectively, wherein at leastone of the first and second insulating layers in the dummy trace portionhas a groove.

In the method of manufacturing the printed circuit board assembly sheet,the at least one of the first and second insulating layers in the dummytrace portion has the groove. This reduces residual stress in the atleast one of the first and second insulating layers in the dummy traceportion. As a result, the printed circuit board assembly sheet isinhibited from being warped.

(8) The step of forming the second insulating layer may include formingthe groove in the second insulating layer in a region between adjacentconductor traces in the dummy trace portion.

In this case, the thickness of the region between the conductor tracesis smaller than the thickness of other portions. This sufficientlyreduces residual stress in the region between the conductor traces. As aresult, the printed circuit board assembly sheet is sufficientlyinhibited from being warped.

(9) The step of forming the first insulating layer may include formingthe groove in the first insulating layer in a region between adjacentconductor traces in the dummy trace portion.

In this case, the thickness of the region between the conductor tracesis smaller than the thickness of other portions. This sufficientlyreduces residual stress in the region between the conductor traces. As aresult, the printed circuit board assembly sheet is sufficientlyinhibited from being warped.

(10) The method of manufacturing the printed circuit board assemblysheet may further include the step of forming an opening in the supportsubstrate in the dummy trace portion. In this case, residual stress isalso reduced in the opening of the support substrate in the dummy traceportion. This sufficiently inhibits the printed circuit board assemblysheet from being warped.

Other features, elements, characteristics, and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments of the present invention with reference to theattached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a top view of a long-sized base material having a plurality ofassembly sheets according to one embodiment of the present invention;

FIG. 2 is an enlarged top view of part of one assembly sheet of FIG. 1;

FIG. 3 is a plan view of one suspension board;

FIG. 4 is a sectional view taken along the line A-A of the assemblysheet of FIG. 2;

FIGS. 5 (a) and (b) are sectional views for illustrating steps in oneexample of a method of manufacturing the assembly sheet according to thepresent embodiment;

FIGS. 6 (a) and (b) are sectional views for illustrating steps in theone example of the method of manufacturing the assembly sheet accordingto the present embodiment;

FIG. 7 is a sectional view showing dimensions of a dummy trace portion;

FIG. 8 is a sectional view showing another example of the configurationof the dummy trace portion;

FIG. 9 is a sectional view showing another example of the configurationof the dummy trace portion;

FIG. 10 is a sectional view showing another example of the configurationof the dummy trace portion;

FIG. 11 is a sectional view showing another example of the configurationof the dummy trace portion;

FIG. 12 is a sectional view showing another example of the configurationof the dummy trace portion;

FIG. 13 is a schematic sectional view of a dummy trace portion of anassembly sheet of a comparative example; and

FIG. 14 is a schematic diagram for illustrating a method of measuring anamount of warp of the assembly sheet.

DETAILED DESCRIPTION OF THE INVENTION

Description will be made of a printed circuit board assembly sheetaccording to embodiments of the present invention with reference to thedrawings. In the present embodiment, a suspension board assembly sheetwith circuits (hereinafter referred to as an assembly sheet) isdescribed as one example of the printed circuit board assembly sheet.

(1) Assembly Sheet

FIG. 1 is a top view of a long-sized base material having a plurality ofassembly sheets according to one embodiment of the present invention.FIG. 2 is an enlarged top view of part of one assembly sheet of FIG. 1.The assembly sheet refers to a half-finished product in the manufactureprocess of the suspension boards with circuits (hereinafter referred toas suspension boards).

In FIG. 1, a direction parallel to a pair of opposite sides of along-sized support substrate 500 is referred to as a longitudinaldirection L, and a direction perpendicular to the longitudinal directionL is referred to as a width direction W. The long-sized supportsubstrate 500 is formed of a metal support substrate.

A plurality of quadrangular assembly sheets 100 are formed in aplurality of columns along the longitudinal direction L on thelong-sized support substrate 500. In the example of FIG. 1, theplurality of assembly sheets 100 are formed in two columns. Theplurality of assembly sheets 100 may be formed in three or more columns,or may be formed in a column on the long-sized support substrate 500. Amethod of manufacturing the assembly sheets 100 will be described below.Each assembly sheet 100 includes a quadrangular support frame FR, aplurality of long-sized suspension boards 1 and two dummy trace portions2. The support frame FR is composed of a pair of end frames f1, f2 thatare parallel to the width direction W and a pair of side frames f3, f4that are parallel to the longitudinal direction L. The plurality ofsuspension boards 1 are formed within the support frame FR. A separationgroove TR is formed along the outer peripheral edge of each suspensionboard 1. The two dummy trace portions 2 are formed in respectiveportions between suspension boards 1 positioned at both ends and the endframes f1, f2 of the support frame FR. Only one dummy trace portion 2may be formed within the support frame FR.

As shown in FIG. 2, a plurality of strip-shaped dummy traces 15 extendin the width direction W in the dummy trace portion 2. Grooves 16 areformed between adjacent dummy traces 15.

Support portions SU are formed between adjacent suspension boards 1within the support frame FR. Both ends of each suspension board 1 arecoupled to the support frame FR with coupling portions J. Side portionsof each suspension board 1 are coupled to the support portion

SU or the dummy trace portion 2 with coupling portions J. In thismanner, the plurality of suspension boards 1 are supported in alignmentalong the longitudinal direction L within the support frame FR.

The coupling portions J are cut in the final stage of the manufacturingsteps, so that each suspension board 1 is separated from the supportframe FR, the support portion SU and the dummy trace portion 2.

(2) Configurations of the Suspension Board 1 and the Dummy Trace Portion2

FIG. 3 is a plan view of one suspension board. FIG. 4 is a sectionalview taken along the line A-A of the assembly sheet 100 of FIG. 2.

As shown in FIG. 3, the suspension board 1 includes a suspension body 1a formed of a support substrate 10 (see FIG. 4) and a base insulatinglayer 11, described below. At the tip of the suspension body 1 a, aU-shaped opening 40 is formed, thereby providing a magnetic headsupporting portion (hereinafter referred to as a tongue) 50. The tongue50 is bent along the broken line R to form a given angle with respect tothe suspension body 1 a.

Four electrode pads 20 are formed at an end of the tongue 50. Fourelectrode pads 30 are formed at the other tip of the suspension body 1a. The four electrode pads 20 on the tongue 50 and the four electrodepads 30 at the other tip of the suspension body 1 a are electricallyconnected to one another through four linear conductor traces 12 thatare wiring traces. A plurality of holes H are formed in the suspensionbody 1 a. The four conductor traces 12 are covered with a coverinsulating layer 13.

FIG. 4 shows cross sections of one suspension board 1 and part of onedummy trace portion 2.

In a region of the suspension board 1, the base insulating layer 11 madeof polyimide is formed on the support substrate 10 made of stainlesssteel. Four conductor traces 12 made of copper are formed on the baseinsulating layer 11. The cover insulating layer 13 made of polyimide isformed to cover the four conductor traces 12.

In the dummy trace portion 2, the plurality of strip-shaped dummy traces15 are formed at spacings on the support substrate 10. Each dummy trace15 includes a strip-shaped base insulating layer 11 made of polyimide, alinear conductor trace 14 made of copper, and a strip-shaped coverinsulating layer 13. The strip-shaped base insulating layers 11 areformed at spacings. The conductor trace 14 is formed on each baseinsulating layer 11, and the cover insulating layer 13 is formed on thebase insulating layer 11 to cover the conductor trace 14. Slit-likegrooves 16 are formed between adjacent dummy traces 15. The baseinsulating layer 11 and the cover insulating layer 13 do not exist inthe groove 16.

In the present embodiment, the conductor traces 14, the dummy traces 15and the grooves 16, each of which has a constant width, in the dummytrace portion 2 continuously and linearly extend from the one side framef3 to the other side frame f4 of the support frame FR of FIG. 2. Thewidth W1 of the support frame FR of FIG. 1 is 35 mm, for example.Preferably, the width W1 is not less than 5 mm and not more than 50 mm,and more preferably not less than 10 mm and not more than 40 mm. Thelength L0 of the support frame FR is 90 mm, for example. Preferably, thelength L0 is not less than 50 mm and not more than 300 mm, and morepreferably not less than 70 mm and not more than 280 mm. The width L1 ofeach of the end frames f1, f2 is 2.4 mm, for example. Preferably, thewidth L1 is not less than 1 mm and not more than 10 mm, and morepreferably not less than 2 mm and not more than 5 mm.

The largest width L2 of the dummy trace portion 2 is 5 mm, for example.Preferably, the largest width L2 is not less than 3 mm and not more than10 mm, and more preferably not less than 4 mm and not more than 7 mm.The smallest width L3 of the dummy trace portion 2 is 2 mm, for example.Preferably, the smallest width L3 is not less than 1.0 mm and not morethan 4 mm, and more preferably not less than 1.5 mm and not more than 3mm.

While the plurality of dummy traces 15 and the plurality of grooves 16are linearly formed parallel to one another in the present embodiment,the present invention is not limited to this. The dummy traces 15 andthe grooves 16 may be each formed in a curved shape. Moreover, the dummytraces 15 and the grooves 16 may not be formed parallel to one another.

(3) Method of Manufacturing the Assembly Sheet 100

Next, description will be made of the method of manufacturing theassembly sheet 100. FIGS. 5 (a), (b) and 6 (a), (b) are sectional viewsfor illustrating steps in one example of the method of manufacturing theassembly sheet 100 according to the present embodiment. FIGS. 5 and 6correspond to the cross section taken along the line A-A of FIG. 2.

First, the base insulating layer 11 made of polyimide is formed on thelong-sized support substrate 10 made of stainless steel as shown in FIG.5 (a). A two-layer base material having a laminated structure of thesupport substrate 10 and the base insulating layer 11 may be used.

The material for the support substrate 10 is not limited to stainlesssteel. For example, another metal material such as aluminum (Al) may beused. The thickness of the support substrate 10 is not less than 5 μmand not more than 50 μm, and preferably not less than 10 μm and not morethan 30 μm, for example. The material for the base insulating layer 11is not limited to polyimide. For example, another resin material such asepoxy may be used. The thickness of the base insulating layer 11 is notless than 3 μm and not more than 20 μm, and preferably not less than 5μm and not more than 15 μm, for example.

The base insulating layer 11 is then subjected to etching with anetching resist (not shown) formed on the base insulating layer 11,thereby forming the base insulating layers 11 for the suspension board 1and the base insulating layers 11 for the plurality of dummy traces 15on the support substrate 10 as shown in FIG. 5 (b).

Next, the conductor traces 12 made of copper are formed on the baseinsulating layers 11 for the suspension board 1, and the conductortraces 14 made of copper are formed on the base insulating layers 11 forthe plurality of dummy traces 15 by electrolytic plating as shown inFIG. 6 (a). The conductor traces 12, 14 may be formed using an additivemethod, a semi-additive method or another method such as a subtractivemethod.

The material for the conductor traces 12, 14 is not limited to copper.For example, another metal such as gold (Au) and aluminum or an alloysuch as a copper alloy and an aluminum alloy may be used. The thicknessof the conductor traces 12 is not less than 3 μm and not more than 16μm, and preferably not less than 6 μm and not more than 13 μm, forexample. The width of the conductor traces 12 is not less than 12 μm andnot more than 60 μm, and preferably not less than 16 μm and not morethan 50 μm, for example.

The cover insulating layer made of polyimide is formed on the supportsubstrate 10 to cover the conductor traces 12, 14 and the baseinsulating layers 11, and the cover insulating layer is then subjectedto etching with an etching resist (not shown) formed on the coverinsulating layer. Thus, the cover insulating layers 13 are formed on thebase insulating layers 11 to cover the conductor traces 12 for thesuspension board 1, and the cover insulating layers 13 are formed on thebase insulating layers 11 to cover the conductor traces 14 for the dummytraces 15 as shown in FIG. 6 (b).

The material for the cover insulating layer 13 is not limited topolyimide. For example, another insulating material such as epoxy may beused. The thickness of the cover insulating layers 13 is not less than 5μm and not more than 30 μm, and preferably not less than 10 μm and notmore than 20 μm, for example.

After that, regions of the support substrate 10 excluding regions of thesuspension bodies 1 a of FIG. 3, the dummy trace portions 2 and thesupport portions SU of FIG. 2 are removed by etching, thereby formingthe separation grooves TR shown in FIG. 2 and the opening 40 and theholes H shown in FIG. 3.

Then, the long-sized support substrate 500 of FIG. 1 is cut, so that theassembly sheets 100 are separated from one another. Accordingly, theindividual assembly sheets 100 are formed. Each of the suspension boards1 is then cut and separated from the support frame FR at the couplingportions J of the assembly sheet 100. In this manner, the plurality ofsuspension boards 1 are completed.

FIG. 7 is a sectional view showing dimensions of the dummy trace portion2. In the dummy trace portion 2 of FIG. 7, the width w1 of the conductortrace 14 is 50 μm, for example. Preferably, the width w1 is not lessthan 20 μm and not more than 200 μm, and more preferably not less than30 μm and not more than 100 μm. The width w2 of the cover insulatinglayer 13 is 120 μm, for example. Preferably, the width w2 is not lessthan 50 μm and not more than 300 μm, and more preferably not less than60 μm and not more than 200 μm. The width w2 of the cover insulatinglayer 13 is equal to the width of the dummy trace 15.

The width w3 of the groove 16 is 320 μm, for example. Preferably, thewidth w3 is not less than 30 μm and not more than 1900 μm, and morepreferably not less than 100 μm and not more than 700 μm. A distance d1between adjacent conductor traces 14 is 250 μm, for example. Preferably,the distance d1 is not less than 100 μm and not more than 2000 μm, andmore preferably not less than 200 μm and not more than 800 μm.

(4) Effects of the Embodiment

In the assembly sheet 100 according to the present embodiment, thegrooves 16 are formed in the base insulating layer 11 and the coverinsulating layer 13 in the dummy trace portion 2. This reduces residualstress in the base insulating layer 11 and the cover insulating layer 13in the dummy trace portion 2. As a result, the assembly sheet 100 isinhibited from being warped.

(5) Other Examples of the Configuration of the Dummy Trace Portion

FIGS. 8 to 12 are sectional views showing other examples of theconfiguration of the dummy trace portion 2. Dummy trace portions inFIGS. 8 to 12 will be described by mainly referring to differences fromthe dummy trace portion 2 of FIG. 7.

In the dummy trace portion 2 of FIG. 8, a slit-like opening 16 a isformed in a region of the support substrate 10 inside each groove 16.The width w4 of the openings 16 a is 70 μm, for example. Preferably, thewidth w4 is not less than 20 μm and not more than 250 μm, and morepreferably not less than 50 μm and not more than 180 μm. The width w5 ofthe support substrate 10 between the openings 16 a is 230 μm, forexample. Preferably, the width w5 is not less than 50 μm and not morethan 2000 μm, and more preferably not less than 110 μm and not more than750 μm.

In this example, the residual stress in the base insulating layer 11 andthe cover insulating layer 13 in the dummy trace portion 2 is reduced,and the residual stress in the support substrate 10 is reduced. As aresult, the assembly sheet 100 is sufficiently inhibited from beingwarped. In the dummy trace portion 2 of FIG. 9, the cover insulatinglayer 13 has the grooves 16, and the base insulating layer 11 does nothave the grooves 16. A plurality of slit-like openings 16 b are formedin the support substrate 10. The plurality of slit-like openings 16 bmay not be formed in regions corresponding to the plurality of grooves16. In the example of FIG. 9, the plurality of slit-like openings 16 bare formed to overlap the dummy traces 15, respectively. In thisexample, the residual stress in the cover insulating layer 13 in thedummy trace portion 2 is reduced, and the residual stress in the supportsubstrate 10 is reduced. As a result, the assembly sheet 100 isinhibited from being warped.

In the dummy trace portion 2 of FIG. 10, similarly to the dummy traceportion 2 of FIG. 9, the cover insulating layer 13 has the grooves 16,and the base insulating layer 11 does not have the grooves 16. Anopening 16 c is formed in the support substrate 10 to overlap a regionincluding the plurality of dummy traces 15 and the plurality of grooves16.

The width w6 of the opening 16 c is 1500 μm, for example. Preferably,the width w6 is not less than 500 μm and not more than 3000 μm, and morepreferably not less than 1000 μm and not more than 2000 μm.

In this example, the residual stress in the cover insulating layer 13 inthe dummy trace portion 2 is reduced, and the residual stress in thesupport substrate 10 is reduced. As a result, the assembly sheet 100 isinhibited from being warped.

In the dummy trace portion 2 of FIG. 11, similarly to the dummy traceportion 2 of FIGS. 9 and 10, the cover insulating layer 13 has thegrooves 16, and the base insulating layer 11 does not have the grooves16. An opening is not formed in the support substrate 10.

In this example, the residual stress is reduced in the cover insulatinglayer 13 in the dummy trace portion 2. As a result, the assembly sheet100 is inhibited from being warped.

In the dummy trace portion 2 of FIG. 12, the base insulating layer 11has the grooves 16, and the cover insulating layer 13 does not have thegrooves 16.

In this example, the residual stress is reduced in the base insulatinglayer 11 in the dummy trace portion 2. As a result, the assembly sheet100 is inhibited from being warped.

(6) Inventive Example

In an inventive example described below, the assembly sheet 100 shown inFIGS. 1 to 7 was formed, and an amount of warp occurred in the assemblysheet 100 was measured. In a comparative example, the assembly sheethaving a dummy trace portion 2 a shown in FIG. 13 was formed, and anamount of warp occurred in the assembly sheet was measured.

In the assembly sheet 100 of the inventive example, the supportsubstrate 10 was made of stainless steel, the base insulating layer 11and the cover insulating layer 13 were made of polyimide, and theconductor traces 12, 14 were made of copper.

The assembly sheet 100 of the inventive example has the width W1 (seeFIG. 1) of 35 mm, and the length L0 of 90 mm. The width L1 of each ofthe end frames f1, f2 of the support frame FR was 2.4 mm, the largestwidth L2 of the dummy trace portion 2 was 5.5 mm, and the smallest widthL3 of the dummy trace portion 2 was 2.5 mm. The width of the conductortraces 12 of the suspension board 1 was 20 μm, the width w1 of theconductor traces 14 in the dummy trace portion 2 was 50 μm, the width w2of each of the base insulating layers 11 and the cover insulating layers13 was 120 μm, the width w3 of the grooves 16 was 320 μm, and thedistance d1 between adjacent conductor traces 14 was 250 μm.

The thickness of the support substrate 10 was 18 μm, the thickness ofthe base insulating layers 11 was 10 μm, the thickness of each of theconductor traces 12, 14 was 12 μm, and the thickness of the coverinsulating layers was 4 μm.

FIG. 13 is a schematic sectional view of the dummy trace portion of theassembly sheet of the comparative example. As shown in FIG. 13, the baseinsulating layer 11 was formed on the support substrate 10 in the dummytrace portion 2 a, and the conductor traces 14 were formed on the baseinsulating layer 11. The cover insulating layer 13 was formed on thebase insulating layer 11 to cover the plurality of conductor traces 14.The base insulating layer 11 and the cover insulating layer 13 do nothave the grooves 16.

The respective materials and dimensions of the parts of the assemblysheet of the comparative example were the same as those of the parts ofthe assembly sheet 100 of the inventive example.

FIG. 14 is a schematic diagram for illustrating a method of measuring anamount of warp of the assembly sheet. As shown in FIG. 14, the assemblysheet 100 was placed on a support stage 600 having a horizontal uppersurface, and the one side frame f3 of the support frame FR was fixed tothe upper surface of the support stage 600 by a fixing member 700. Inthis state, the height from the upper surface of the support stage 600to an end edge of the other side frame f4 of the assembly sheet 100 wasmeasured as the amount of warp h. The amount of warp h of the assemblysheet of the comparative example was measured in the same manner.

Respective amounts of warp h of six test samples were measured for theassembly sheet 100 of the inventive example, and the average of theamounts of warp h of the six test samples was calculated. Similarly,respective amounts of warp h of six test samples were measured for theassembly sheet of the comparative example, and the average of theamounts of warp h of the six test samples was calculated. Results of themeasurements are shown in Table 1.

TABLE 1 AMOUNT OF WARP h [mm] TEST INVENTIVE COMPARATIVE SAMPLE EXAMPLEEXAMPLE 1 0.4 1.1 2 0.5 1.2 3 0.5 1.0 4 0.6 1.2 5 0.4 1.1 6 0.4 1.1AVERAGE 0.47 1.12

As shown in Table 1, the average of the amounts of warp h of theassembly sheet 100 of the inventive example was 0.47 mm, and the averageof the amounts of warp h of the assembly sheet of the comparativeexample was 1.12 mm. As seen from the above, the amount of warp h of theassembly sheet 100 of the inventive example was as low as 42% of theamount of warp h of the assembly sheet of the comparative example.

It can be seen from the result that the amount of warp in the assemblysheet 100 is reduced by forming the grooves 16 in the dummy traceportion 2 of the assembly sheet 100.

(7) Other Embodiments

While the grooves 16 in the dummy trace portion 2 penetrate the coverinsulating layer 13 from the upper surface to the lower surface of thecover insulating layer 13 or penetrate the base insulating layer 11 fromthe upper surface to the lower surface of the base insulating layer 11in the foregoing embodiment, the present invention is not limited tothis. The grooves 16 in the dummy trace portion 2 may be formed in thecover insulating layer 13 so as to have a given depth from the uppersurface of the cover insulating layer 13, or may be formed in the baseinsulating layer 11 so as to have a given depth from the upper surfaceof the base insulating layer 11.

While the grooves 16 in the dummy trace portion 2 continuously extendfrom the one side frame f3 to the other side frame f4 of the supportframe FR in the foregoing embodiment, the present invention is notlimited to this. The grooves 16 in the dummy trace portion 2 may beinterrupted within the support frame FR.

While the slit-like openings 16 a, 16 b, 16 c continuously extend fromthe one side frame f3 to the other side frame f4 of the support frame FRin the support substrate 10 in the dummy trace portion 2 in the examplesof FIGS. 8, 9 and 10, the present invention is not limited to this. Theopenings 16 a, 16 b, 16 c may be interrupted within the support frame FRin the support substrate 10 in the dummy trace portion 2.

While each of the conductor traces 14 in the dummy trace portion 2 has aconstant width in the foregoing embodiment, the present invention is notlimited to this. Each of the conductor traces 14 in the dummy traceportion 2 may have different widths in different portions in itslongitudinal direction.

While each of the grooves 16 in the dummy trace portion 2 has a constantwidth in the foregoing embodiment, the present invention is not limitedto this. Each of the grooves 16 in the dummy trace portion 2 may havedifferent widths in different portions in its longitudinal direction.While each of the openings 16 a, 16 b, 16 c of the support substrate 10in the dummy trace portion 2 has a constant width in the examples ofFIGS. 8, 9 and 10, the present invention is not limited to this. Each ofthe openings 16 a, 16 b, 16 c of the support substrate 10 in the dummytrace portion 2 may have different widths in different portions in itslongitudinal direction.

While the assembly sheet 100 has the quadrangular shape in the foregoingembodiment, the present invention is not limited to this. For example,the assembly sheet 100 may have another shape such as an ellipticalshape or a triangular shape.

While the dummy trace portion 2 has a substantially trapezoidal shape inthe foregoing embodiment, the present invention is not limited to this.The shape of the dummy trace portion 2 varies according to the shape ofthe printed circuit board. The dummy trace portion 2 may have arectangular shape or a triangular shape, for example.

While the grooves 16 in the dummy trace portion 2 are not formed in thesupport frame FR in the foregoing embodiment, the grooves 16 may beformed in the support frame FR.

While the printed circuit board assembly sheet is the suspension boardassembly sheet with circuit in the foregoing embodiment, the printedcircuit boards of the printed circuit board assembly sheet according tothe present invention is not limited to the suspension boards withcircuits. For example, the printed circuit boards may be other printedcircuit boards such as flexible printed circuit boards, substrates forCOF (Chip On Film) and substrates for TAB (Tape Automated Bonding).

(8) Correspondences between Elements in the Claims and Parts inEmbodiments

In the following paragraphs, non-limiting examples of correspondencesbetween various elements recited in the claims below and those describedabove with respect to various preferred embodiments of the presentinvention are explained.

In the above-described embodiments, the assembly sheet 100 is an exampleof a printed circuit board assembly sheet, the suspension board withcircuit 1 is an example of a printed circuit board, the support frame FRis an example of a support frame, the dummy trace portion 2 is anexample of a dummy trace portion, and the groove 16 is an example of aseparation groove.

The support substrate 10 is an example of a support substrate, the baseinsulating layer 11 is an example of a first insulating layer, theconductor traces 12, 14 are examples of a conductor trace, and the coverinsulating layer 13 is an example of a second insulating layer.

The openings 16 a, 16 b, 16 c are examples of an opening, the sideframes f3, f4 are an example of a pair of first frames, and the endframes f1, f2 are an example of a pair of second frames.

As each of various elements recited in the claims, various otherelements having configurations or functions described in the claims canbe also used.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

I/we claim:
 1. A method of manufacturing a printed circuit boardassembly sheet comprising a plurality of printed circuit boards, asupport frame configured to integrally support the plurality of printedcircuit boards such that the plurality of printed circuit boards arearranged at spacings, and a dummy trace portion provided in a regionbetween at least one printed circuit board on one end side and thesupport frame, the method comprising the steps of: forming firstinsulating layers, which correspond to the plurality of printed circuitboards and the dummy trace portion, on a support substrate; forming aplurality of conductor traces on each of the first insulating layerscorresponding to the plurality of printed circuit boards and the firstinsulating layer corresponding to the dummy trace portion; and formingsecond insulating layers on the first insulating layers to cover theplurality of conductor traces corresponding to the plurality of printedcircuit boards and the conductor trace corresponding to the dummy traceportion, respectively, wherein at least one of the first and secondinsulating layers in the dummy trace portion has a groove.
 2. The methodof manufacturing the printed circuit board assembly sheet according toclaim 1, wherein each of the plurality of printed circuit boards isconfigured to be separated from the support frame, and the dummy traceportion is configured not to be separated from the support frame.
 3. Themethod of manufacturing the printed circuit board assembly sheetaccording to claim 1, wherein the groove is not formed in the firstinsulating layer in a region between adjacent conductor traces in thedummy trace portion, and wherein the step of forming the secondinsulating layers includes forming the groove in the second insulatinglayer in the region between the adjacent conductor traces in the dummytrace portion.
 4. The method of manufacturing the printed circuit boardassembly sheet according to claim 2, wherein the groove is not formed inthe first insulating layer in a region between adjacent conductor tracesin the dummy trace portion, and wherein the step of forming the secondinsulating layers includes forming the groove in the second insulatinglayer in the region between the adjacent conductor traces in the dummytrace portion.
 5. The method of manufacturing the printed circuit boardassembly sheet according to claim 1, wherein the step of forming thefirst insulating layers includes forming the groove in the firstinsulating layer in a region between adjacent conductor traces in thedummy trace portion, and wherein the groove is not formed in the secondinsulating layer in the region between the adjacent conductor traces inthe dummy trace portion.
 6. The method of manufacturing the printedcircuit board assembly sheet according to claim 2, wherein the step offorming the first insulating layers includes forming the groove in thefirst insulating layer in a region between adjacent conductor traces inthe dummy trace portion, and wherein the groove is not formed in thesecond insulating layer in the region between the adjacent conductortraces in the dummy trace portion.
 7. The method of manufacturing theprinted circuit board assembly sheet according to claim 1, wherein thestep of forming the first insulating layers includes forming the groovein the first insulating layer in a region between adjacent conductortraces in the dummy trace portion, and wherein the step of forming thesecond insulating layers includes forming the groove in the secondinsulating layer in the region between the adjacent conductor traces inthe dummy trace portion.
 8. The method of manufacturing the printedcircuit board assembly sheet according to claim 2, wherein the step offorming the first insulating layers includes forming the groove in thefirst insulating layer in a region between adjacent conductor traces inthe dummy trace portion, and wherein the step of forming the secondinsulating layers includes forming the groove in the second insulatinglayer in the region between the adjacent conductor traces in the dummytrace portion.
 9. The method of manufacturing the printed circuit boardassembly sheet according to claim 1, further comprising the step offorming an opening in the support substrate in the dummy trace portion.10. The method of manufacturing the printed circuit board assembly sheetaccording to claim 1, wherein the support frame has a pair of firstframe portions that are substantially parallel to each other and a pairof second frame portions that are substantially perpendicular to thefirst frame portions, the plurality of printed circuit boards beingprovided to be arranged in a direction parallel to the pair of firstframe portions, and wherein the dummy trace portion is provided in theregion between at least the printed circuit board on the one end sideand one of the pair of second frame portions, the conductor traces andthe groove in the dummy trace portion being formed to extend in adirection from one of the first frame portions to the other one of thefirst frame portions.
 11. The method of manufacturing the printedcircuit board assembly sheet according to claim 1, wherein the printedcircuit board is a suspension board with circuits.